Epoxidized fatty acid methyl ester as low-shear rheology modifier for invert emulsion oil based mud

ABSTRACT

An invert oil-based mud (OBM) may include an oleaginous continuous phase, an aqueous internal phase, an emulsifier; and a rheology modifier. The rheology modifier may include one or more of the group consisting of epoxidized methyl oleate, epoxidized methyl linoleate, and epoxidized methyl α-linolenate. The invert OBM may contain the rheology modifier in an amount of the range of 0.1 to 5 wt. % (weight percent) relative to the total weight of the OBM.

BACKGROUND

Wellbore drilling operations may use wellbore fluids for multiple purposes including, for example, cooling the drill bit and transporting wellbore cuttings to the surface. Drilling fluids are also used to reduce friction between the drill string and the casing or the wellbore wall by functioning as a lubricating medium. Drilling fluids can be divided into a variety of categories including, for example, oil-based drilling fluids and water-based drilling fluids. Additives may be included to enhance the properties of the fluids.

Although water-based muds (WBMs) are often preferred due to environmental concerns that are associated with oil-based muds (OBMs), they may not be viable for use in certain high pressure and high temperature (HPHT) sections of a wellbore. This leads to the employment of OBMs, including invert emulsion OBMs, which may be more stable under such conditions. OBMs can also provide improved shale inhibition as compared to WBMs, and so are also preferred when drilling wellbore sections that contain reactive shale. Invert emulsion OBMs may be formulated to include additives, such as emulsifiers, which aid in the formation of a stable water-in-oil (W/O) emulsion, and rheology modifiers, which allow for tuning the rheological properties of the fluid.

SUMMARY

This summary is provided to introduce a selection of concepts that are further described in the detailed description. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in limiting the scope of the claimed subject matter.

In one aspect, embodiments disclosed relate to an invert oil-based mud (OBM) that includes an oleaginous continuous phase, an aqueous internal phase, an emulsifier; and a rheology modifier. The rheology modifier may include one or more of the group consisting of epoxidized methyl oleate, epoxidized methyl linoleate, and epoxidized methyl α-linolenate.

In another aspect, embodiments disclosed relate to methods of using an invert oil-based mud (OBM) in a wellbore that include introducing the invert OBM into the wellbore. The invert OBM may include an oleaginous continuous phase; an aqueous internal phase; an emulsifier; and a rheology modifier. The rheology modifier may include one or more selected from the group consisting of epoxidized methyl oleate, epoxidized methyl linoleate, and epoxidized methyl alpha-linolenate.

In a further aspect, embodiments disclosed relate to methods of preparing an invert oil-based mud (OBM), the methods including forming a rheology modifier by epoxidizing linseed oil and transesterifying the epoxidized linseed oil with methanol, and mixing the rheology modifier with an emulsifier, an oleaginous phase, and an aqueous phase.

Other aspects and advantages of the claimed subject matter will be apparent from the description, the drawings, and the claims that follow.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1A-B depict the chemical structures of an epoxidized triglyceride (FIG. 1A) and epoxidized fatty acid methyl esters (FIG. 1B) of one or more embodiments, which are derived from linseed oil.

FIG. 2 is a schematic representation of a method of producing an invert emulsion OBM of one or more embodiments.

FIG. 3 is a graphical representation of the low-shear rheology of exemplary wellbore fluids.

FIG. 4 is a graphical representation of the 10 second and 10 minute gel strength of exemplary wellbore fluids.

DETAILED DESCRIPTION

Embodiments in accordance with the present disclosure generally relate to rheology modifiers and their preparation, wellbore fluids that contain said rheology modifiers, and methods of using said wellbore fluids. Generally, the rheology modifiers of one or more embodiments disclosed comprise one or more epoxidized fatty acid esters.

The suitability of a wellbore fluid for its use in a given application is significantly determined by its rheological properties, including its plastic viscosity, gel strength, yield point, and low shear rate rheology. These properties may be altered by the inclusion of rheology modifiers. Rheology modifiers are of particular importance in drilling fluids because the low-shear rheology of the fluid is directly relevant in determining the ability of the fluid to suspend solids, such as weighting materials and drill cuttings, enabling their removal from the wellbore.

Rheology Modifiers

Rheology modifiers in accordance with one or more embodiments of the present disclosure comprise one or more epoxidized fatty acid esters. These epoxidized fatty acid esters may be derived from a vegetable oil. The vegetable oil of some embodiments may be a triglyceride extracted from a plant. A triglyceride is an ester of glycerol and three fatty acids. Depending on the plant from which it is derived, a vegetable oil may contain a mixture of different types of fatty acids, including, for example, saturated, mono unsaturated, poly unsaturated, omega 3, omega 6, and omega 9 fatty acids. The presence of these different types of fatty acids makes vegetables a promising source for rheology modifiers for drilling fluids. In some embodiments, the rheology modifiers of the present disclosure may be derived from unused or unprocessed vegetable oils, such as virgin, fresh, or raw oils. In other embodiments, the rheology modifiers of the present disclosure may be derived from waste vegetable oils that have been used for a different process, such as cooking or other food preparations, prior to the preparation of the rheology modifier.

Rheology modifiers in accordance with one or more embodiments of the present disclosure may contain epoxidized fatty acid esters that are derived from linseed oil. Linseed oil (which is also commonly known as flaxseed oil) is a natural oil that is derived from the seeds of the flax plant. It is widely used as an impregnator for various materials, as a drying oil or varnish, as a pigment binder, as a plasticizer, and as a nutritional supplement. Linseed oil comprises a triglyceride containing three different unsaturated fatty acids, namely oleic, linoleic acid and α-linolenic acid. Linseed oil may further contain smaller amounts of saturated fatty acids such as palmitic acid and stearic acid in addition to one or more unsaturated fatty acids.

The rheology modifier of one or more embodiments particularly comprises one or more epoxidized fatty acid esters. These epoxidized fatty acid esters may be prepared by first epoxidizing an unsaturated triglyceride to give an epoxidized triglyceride. Where, for instance, the triglyceride is linseed oil, the resulting epoxidized triglyceride may be epoxidized linseed oil as depicted in FIG. 1A. The epoxidized triglyceride may contain fatty acids having a carbon chain ranging in length from C6 to C32. For example, the epoxidized triglyceride may contain fatty acids having a carbon chain having a length ranging from a lower limit of any of 6, 8, 10, 12, 14, 16, and 18 carbons to an upper limit of any of 18, 20, 22, 24, 26, 28, 30, and 32 carbons, where any lower limit can be used in combination with any mathematically-compatible upper limit. Transesterifying the epoxidized triglyceride by reaction with an alcohol yields the corresponding epoxidized fatty acid esters. The particular alcohol used for the transesterification may not be particularly limited. In some embodiments, the alcohol may be one or more selected from the group consisting of methanol, ethanol, propanol, butanol, petanol, and isomers and derivatives thereof. In particular embodiments, the alcohol may be methanol, and the resulting epoxidized fatty acid esters may be epoxidized fatty acid methyl esters (“EME-FA”).

In embodiments where the triglyceride is linseed oil and the alcohol is methanol, the resulting rheology modifier will comprise the epoxidized methyl ester of oleic acid (also known as epoxidized methyl oleate), the epoxidized methyl ester of linoleic acid (also known as epoxidized methyl linoleate), and the epoxidized methyl ester of α-linolenic acid (also known as epoxidized methyl α-linolenate), as depicted in FIG. 1B. In some embodiments, the EME-FA may be a commercial product, such as VIKOFLEX® 9010 (Arkema; King of Prussia, Pa.).

The rheology modifier of one or more embodiments may comprise an ester of oleic acid, an ester of linoleic acid, and an ester of α-linolenic acid. In some embodiments, the rheology modifier may consist essentially of an epoxidized ester of oleic acid, an epoxidized ester of linoleic acid, and an epoxidized ester of α-linolenic acid. In some embodiments, the rheology modifier may consist of an epoxidized ester of oleic acid, an epoxidized ester of linoleic acid, and an epoxidized ester of α-linolenic acid.

In embodiments where the rheology modifier is derived from linseed oil, the rheology modifier may comprise an epoxidized ester of oleic acid, an epoxidized ester of linoleic acid, and an epoxidized ester of α-linolenic acid, in relative amounts that reflect the content of each of oleic acid, linoleic acid, and α-linolenic acid in the linseed oil.

The rheology modifier of one or more embodiments may contain an epoxidized ester of oleic acid in an amount of the range of about 1 to 30% by weight (wt. %). For example, the rheology modifier may contain the epoxidized ester of oleic acid in an amount ranging from a lower limit of any of 1, 2, 5, 10, 12, 15, 18, and 20 wt. % to an upper limit of any of 10, 12, 15, 18, 20, 22, 25, and 30 wt. %, where any lower limit can be used in combination with any mathematically-compatible upper limit.

The rheology modifier of one or more embodiments may contain an epoxidized ester of linoleic acid in an amount of the range of about 1 to 30 wt. %. For example, the rheology modifier may contain the epoxidized ester of linoleic acid in an amount ranging from a lower limit of any of 1, 2, 5, 10, 12, 15, 18, and 20 wt. % to an upper limit of any of 10, 12, 15, 18, 20, 22, 25, and 30 wt. %, where any lower limit can be used in combination with any mathematically-compatible upper limit.

The rheology modifier of one or more embodiments may contain an epoxidized ester of α-linolenic acid in an amount of the range of about 30 to 70 wt. %. For example, the rheology modifier may contain the epoxidized ester of α-linolenic acid in an amount ranging from a lower limit of any of 30, 35, 40, 45, 50, 55, and 60 wt. % to an upper limit of any of 40, 45, 50, 55, 60, 65, and 70 wt. %, where any lower limit can be used in combination with any mathematically-compatible upper limit.

Wellbore Fluids

One or more embodiments of the present disclosure relate to wellbore fluids and may include, for example, water-based wellbore fluids, invert emulsion wellbore fluids, and oil-based wellbore fluids. The wellbore fluids may be drilling fluids, such as oil-based drilling muds (OBMs).

Oil-based wellbore fluids of one or more embodiments may have an oleaginous base fluid. The oleaginous fluid may be a natural or synthetic oil. In one or more embodiments, the oleaginous fluid may be one or more of diesel oil, mineral oil, polyalphaolefins, siloxanes, organosiloxanes, fatty acid esters, and mixtures thereof.

The wellbore fluid of one or more embodiments may comprise a rheology modifier in an amount ranging from about 0.1 to about 10% by volume (vol. %). For example, the wellbore fluid may contain the rheology modifier in an amount ranging from a lower limit of any of 0.1, 0.3, 0.5, 0.7, 1.0, 1.2, 1.5, 2.0, 2.5, 3.0, and 5.0 vol. % to an upper limit of any of 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 5.0, 7.5, and 10 vol. %, where any lower limit can be used in combination with any mathematically-compatible upper limit. In particular embodiments, the wellbore fluid may contain the rheology modifier in an amount of about 1.0 to about 3.0 vol. %.

The wellbore fluid of one or more embodiments may comprise a rheology modifier in an amount ranging from about 0.1 to about 5 wt. %. For example, the wellbore fluid may contain the rheology modifier in an amount ranging from a lower limit of any of 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 1.0, 1.2, 1.5, 2.0, 2.5, and 3.0 wt. % to an upper limit of any of 0.5, 0.6, 0.8, 1.0, 1.2, 1.4, 1.6, 1.8, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, and 5.0 wt. %, where any lower limit can be used in combination with any mathematically-compatible upper limit. In particular embodiments, the wellbore fluid may contain the rheology modifier in an amount of about 0.5 to 1.5 wt. %.

Wellbore fluids of one or more embodiments may be emulsions that comprise both an oleaginous external phase and a non-oleaginous internal phase. The oleaginous external phase may comprise one or more of the oleaginous fluids described previously. The non-oleaginous internal phase may be an aqueous fluid. The aqueous fluid may include at least one of fresh water, synthetic or natural seawater, synthetic or natural brine, formation water, production water, brackish water, each of which may contain water-soluble organic compounds or minerals, or both, and mixtures thereof. The aqueous fluid may be fresh water that is formulated to contain various salts. The salts may include, but are not limited to, alkali metal halides and hydroxides. In one or more embodiments of the wellbore fluid disclosed, the brine may be any of seawater, aqueous solutions where the salt concentration is less than that of sea water, or aqueous solutions where the salt concentration is greater than that of seawater. Salts that may be found in seawater may include salts that produce disassociated ions of sodium, calcium, aluminium, magnesium, potassium, strontium, and lithium salts of halides, carbonates, chlorates, bromates, nitrates, oxides, and phosphates, among others. In some embodiments, the brine may include one or more of the group consisting of an alkali metal halide, an alkali metal carboxylate salt, an alkaline earth metal halide, and an alkaline earth metal carboxylate salt. In particular embodiments, the brine may comprise calcium chloride. Any of the aforementioned salts may be included in brine.

In one or more embodiments, the density of aqueous fluid, and, in turn, the wellbore fluid, may be controlled by increasing the salt concentration. The maximum concentration is determined by the solubility of the salt.

In some embodiments, wellbore fluids may be invert emulsions that have an oleaginous external phase and a non-oleaginous internal phase. The invert emulsion of one or more embodiments may contain a volume ratio of the oleaginous phase to the non-oleaginous phase ranging from about 30:70 to about 99:1. For example, the invert emulsion may have a volume ratio of the oleaginous phase to the non-oleaginous phase ranging from a lower limit of any of 30:70, 40:60, 50:50, 60:40, 70:30, 80:20, and 90:10 to an upper limit of any 40:60, 50:50, 60:40, 70:30, 80:20, 90:10, 95:5, and 99:1, where any lower limit can be used in combination with any mathematically-compatible upper limit.

In one or more embodiments, wellbore fluids may contain one or more emulsifiers. A first, or primary, emulsifier may be added to create a stable emulsion of water in oil. The primary emulsifier can reduce interfacial tension between the oleaginous and nonoleaginous phases and increase the emulsion stability of the drilling fluid. The primary emulsifier of one or more embodiments is not particularly limited, but may be a fatty acid derivative such as INVERMUL® (Halliburton; Houston, Tex.).

The wellbore fluid of one or more embodiments may comprise a primary emulsifier in an amount ranging from about 0.1 to about 20 vol. %. For example, the wellbore fluid may contain the primary emulsifier in an amount ranging from a lower limit of any of 0.1, 0.3, 0.5, 0.7, 1.0, 1.2, 1.5, 2.0, 2.5, 3.0, 4.0, 5.0, and 10.0 vol. % to an upper limit of any of 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 10.0, 12.5, 15.0, 17.5, and 20.0 vol. %, where any lower limit can be used in combination with any mathematically-compatible upper limit. In particular embodiments, the wellbore fluid may contain the primary emulsifier in an amount of about 1.0 to about 6.0 vol. %.

The wellbore fluid of one or more embodiments may comprise a primary emulsifier in an amount ranging from about 0.1 to about 10 wt. %. For example, the wellbore fluid may contain the primary emulsifier in an amount ranging from a lower limit of any of 0.1, 0.3, 0.5, 0.7, 1.0, 1.2, 1.5, 2.0, 2.5, 3.0, and 5.0 wt. % to an upper limit of any of 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 5.0, 7.5, and 10 wt. %, where any lower limit can be used in combination with any mathematically-compatible upper limit. In particular embodiments, the wellbore fluid may contain the primary emulsifier in an amount of about 1.0 to about 3.0 wt. %.

In one or more embodiments, wellbore fluids may contain an additional, or secondary, emulsifier. The secondary emulsifier may be utilized to consolidate the stability of the dispersed phase or the overall emulsion. The secondary emulsifier of one or more embodiments is not particularly limited but, as would be understood by a person of ordinary skill in the art, is generally selected to be compatible with the primary emulsifier. In some embodiments, the secondary emulsifier may be EZ MUL® (Halliburton; Houston, Tex.).

The wellbore fluid of one or more embodiments may comprise a secondary emulsifier in an amount ranging from about 0.1 to about 10% by volume (vol. %). For example, the wellbore fluid may contain the secondary emulsifier in an amount ranging from a lower limit of any of 0.1, 0.3, 0.5, 0.7, 1.0, 1.2, 1.5, 2.0, 2.5, 3.0, and 5.0 vol. % to an upper limit of any of 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 5.0, 7.5, and 10 vol. %, where any lower limit can be used in combination with any mathematically-compatible upper limit. In particular embodiments, the wellbore fluid may contain the secondary emulsifier in an amount of about 0.5 to about 2.0 vol. %.

The wellbore fluid of one or more embodiments may comprise a secondary emulsifier in an amount ranging from about 0.1 to about 5 wt. %. For example, the wellbore fluid may contain the secondary emulsifier in an amount ranging from a lower limit of any of 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 1.0, 1.2, 1.5, 2.0, 2.5, and 3.0 wt. % to an upper limit of any of 0.5, 0.6, 0.8, 1.0, 1.2, 1.4, 1.6, 1.8, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, and 5.0 wt. %, where any lower limit can be used in combination with any mathematically-compatible upper limit. In particular embodiments, the wellbore fluid may contain the secondary emulsifier in an amount of about 0.1 to about 1.0 wt. %.

Further, other additives may be included in the wellbore fluids of the present disclosure. Such additives may include, for instance, one or more of the group consisting of weighting agents, pH adjusting agents, additional rheology modifiers (or viscosifiers), wetting agents, corrosion inhibitors, oxygen scavengers, anti-oxidants, biocides, surfactants, dispersants, interfacial tension reducers, mutual solvents, thinning agents, and combinations thereof. The identities and use of the aforementioned additives are not particularly limited. One of ordinary skill in the art will, with the benefit of this disclosure, appreciate that the inclusion of a particular additive will depend upon the desired application, and properties, of a given wellbore fluid.

Weighting agents suitable for use in the wellbore fluids of one or more embodiments include, for example, bentonite, barite, dolomite, calcite, aragonite, iron carbonate, zinc carbonate, manganese tetroxide, zinc oxide, zirconium oxide hematite, ilmenite, lead carbonate, and combinations thereof.

The pH adjusting agents that are included in the wellbore fluids of one or more embodiments may be one or more alkaline compounds. In one or more embodiments, suitable alkaline compounds include alkali metal and alkaline metal salts such as, lime, soda ash, sodium hydroxide, potassium hydroxide, and combinations thereof.

The wellbore fluid of one or more embodiments may comprise a pH adjusting agent in an amount ranging from about 0.1 to about 5 wt. %. For example, the wellbore fluid may contain the pH adjusting agent in an amount ranging from a lower limit of any of 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 1.0, 1.2, 1.5, 2.0, 2.5, and 3.0 wt. % to an upper limit of any of 0.5, 0.6, 0.8, 1.0, 1.2, 1.4, 1.6, 1.8, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, and 5.0 wt. %, where any lower limit can be used in combination with any mathematically-compatible upper limit. In particular embodiments, the wellbore fluid may contain the pH adjusting agent in an amount of about 0.5 to about 1.5 wt. %.

The viscosifiers that are included in the wellbore fluids of one or more embodiments may be selected from the group consisting of organophilic clays, hectorite clays, dimeric and trimeric fatty acids, polyamines, and sepiolite. In some embodiments, the viscosifier may be GELTONE® II (Halliburton; Houston, Tex.).

The wellbore fluid of one or more embodiments may comprise a viscosifier in an amount ranging from about 0.1 to about 5 wt. %. For example, the wellbore fluid may contain the viscosifier in an amount ranging from a lower limit of any of 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 1.0, 1.2, 1.5, 2.0, 2.5, and 3.0 wt. % to an upper limit of any of 0.5, 0.6, 0.8, 1.0, 1.2, 1.4, 1.6, 1.8, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, and 5.0 wt. %, where any lower limit can be used in combination with any mathematically-compatible upper limit. In particular embodiments, the wellbore fluid may contain the viscosifier in an amount of about 0.1 to about 1.0 wt. %.

The filtration control agents that are included in the wellbore fluids of one or more embodiments may be selected from the group consisting of modified lignites, asphalts or gilsonites, and nonaqueous polymeric fluids. In some embodiments, the filtration control agent may be DURATONE® HT (Halliburton; Houston, Tex.)

The wellbore fluid of one or more embodiments may comprise a filtration control agent in an amount ranging from about 0.1 to about 5 wt. %. For example, the wellbore fluid may contain the filtration control agent in an amount ranging from a lower limit of any of 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 1.0, 1.2, 1.5, 2.0, 2.5, and 3.0 wt. % to an upper limit of any of 0.5, 0.6, 0.8, 1.0, 1.2, 1.4, 1.6, 1.8, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, and 5.0 wt. %, where any lower limit can be used in combination with any mathematically-compatible upper limit. In particular embodiments, the wellbore fluid may contain the filtration control agent in an amount of about 0.5 to about 1.5 wt. %.

A method of preparing an invert OBM of one or more embodiments is depicted by FIG. 2. All components and quantities discussed in relation to said method correspond to those discussed previously. At 200, a rheology modifier is prepared from a vegetable oil. For example, the rheology modifier may be prepared from linseed oil as discussed previously. In one or more embodiments, the rheology modifier may comprise one or more epoxidized fatty acid esters, such as an ester of epoxidized oleic acid, an ester of epoxidized linoleic acid, and an ester of epoxidized α-linolenic acid.

At 210, a quantity of the rheology modifier and a quantity of one or more emulsifiers are added to an oleaginous base fluid. At 220, a quantity of an optional additive, such as a pH adjusting agent, may also be added to the oleaginous base fluid. At 230, a quantity of a nonoleaginous fluid is added to the oleaginous fluid to which the previously mentioned components have been added. At 240, a quantity of an additive, such as a weighting agent is added to the aforementioned components. At 250, the inverted oil-based drilling fluid mixed with the previously mentioned components is used in a wellbore drilling operation to drill a wellbore in a subterranean zone. For example, multiple barrels of the oil-based drilling fluid are prepared, each barrel mixed with the previously-mentioned components. The multiple barrels are flowed through a subterranean zone while drilling a wellbore in the subterranean zone.

The physical properties of a wellbore fluid are important in determining the suitability of the fluid for a given application.

The wellbore fluid of one or more embodiments may have a density that is greater than 60 lb/ft³ (pounds per cubic foot). For example, the wellbore fluid may have a density that is of an amount ranging from a lower limit of any of 60, 62, 64, 66, 68, 70, 75, and 80 lb/ft³ to an upper limit of any of 66, 70, 80, 90, 100, 110, 120, 130, 140, 150 and 160 lb/ft³, where any lower limit can be used in combination with any mathematically-compatible upper limit.

Rheological features such as plastic viscosity (PV), yield point (YP), initial gel strength, and final gel strength can be determined for a wellbore fluid. The values described may be determined for a wellbore fluid after hot-rolling at, for instance, 300° F. for 16 h (hours) under a pressure of 500 psi (pounds per square inch). The values were obtained from a viscometer at dial readings of 600 rpm (revolutions per minute) and 300 rpm. To measure the initial and final gel strength of a wellbore fluid, a viscometer can be operated at 600 rpm for 10 s (seconds) and then switched off for 10 s and 10 min (minutes), respectively. Afterward, the viscometer can be turned to a revolution speed of 3 rpm to provide the gel strength reading.

The YP and PV are parameters from the Bingham Plastic rheology (BP) model. The plastic viscosity of a fluid is a measure of the resistance of the fluid to flow. For instance, drilling fluids that have a reduced plastic viscosity have the capacity to drill more quickly than drilling fluids with a greater PV value. Plastic viscosity is dependent on both the solid content of a fluid and temperature. The wellbore fluid of one or more embodiments may have a plastic viscosity ranging from about 1 to 40 cP (centipoise). For example, the wellbore fluid may have a plastic viscosity that ranges from a lower limit of any of 1, 5, 10, 15, 20, 25, and 30 cP to an upper limit of any of 20, 25, 30, 35, and 40 cP, where any lower limit can be used in combination with any mathematically-compatible upper limit.

The YP is determined by extrapolating the BP model to a shear rate of zero; it represents the stress required to move the fluid. The yield point is the resistance of a fluid to initiate movement and is an assessment of the strength of the attractive forces between the colloidal particles of the fluid. The yield point, for instance, demonstrates the capability of a drilling fluid to raise shale cuttings out of a wellbore under dynamic conditions. A fluid with a greater yield point may provide a better carrying capacity as compared to a fluid with similar density and a reduced yield point. The wellbore fluid of one or more embodiments may have a yield point ranging from about 5 to 15 lb/100 ft² (pounds per 100 square feet). For example, the wellbore fluid may have a yield point that ranges from a lower limit of any of 5, 6, 7, 8, 9, and 10 lb/100 ft² to an upper limit of any of 10, 11, 12, 13, 14, and 15 lb/100 ft², where any lower limit can be used in combination with any mathematically-compatible upper limit.

The wellbore fluid of one or more embodiments may have an initial gel strength, after 10 seconds, ranging from about 5 to about 20 lb/100 ft². For example, the wellbore fluid may have an initial gel strength that ranges from a lower limit of any of 5, 6, 7, 8, 9, and 10 lb/100 ft² to an upper limit of any of 9, 10, 12, 15, and 20 lb/100 ft², where any lower limit can be used in combination with any mathematically-compatible upper limit.

The wellbore fluid of one or more embodiments may have a final gel strength, after 10 minutes, ranging from about 5 to about 30 lb/100 ft². For example, the wellbore fluid may have a final gel strength that ranges from a lower limit of any of 5, 7, 9, 10, 11, 12, 13, 15, and 20 lb/100 ft² to an upper limit of any of 13, 15, 18, 20, 25, and 30 lb/100 ft², where any lower limit can be used in combination with any mathematically-compatible upper limit.

The wellbore fluid of one or more embodiments may have a 3-rpm viscometer reading ranging from about 1 to about 15 cP. For example, the wellbore fluid may have a plastic viscosity that ranges from a lower limit of any of 1, 2, 3, 4, 5, 6, and 8 cP to an upper limit of any of 6, 8, 10, 12, and 15 cP, where any lower limit can be used in combination with any mathematically-compatible upper limit.

The wellbore fluid of one or more embodiments may have a 6-rpm viscometer reading ranging from about 5 to about 20 cP. For example, the wellbore fluid may have a plastic viscosity that ranges from a lower limit of any of 5, 6, 7, 8, 9 and 10 cP to an upper limit of any of 7, 8, 9, 10, 12, 15, and 20 cP, where any lower limit can be used in combination with any mathematically-compatible upper limit.

The apparent viscosity of a fluid is directly related to the swelling rate of the fluid in the presence of an inhibition medium. Therefore, a low apparent viscosity demonstrates that the fluid may have a reduced interaction with clay. The wellbore fluid of one or more embodiments may have an apparent viscosity ranging from about 10 to about 150 cP. For example, the wellbore fluid may have an apparent viscosity that ranges from a lower limit of any of 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 90 and 100 cP to an upper limit of any of 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, and 150 cP, where any lower limit can be used in combination with any mathematically-compatible upper limit.

Methods

Wellbore fluids of one or more embodiments may be introduced into a wellbore or subterranean formation using techniques known to a person of ordinary skill in the art. The wellbore fluids of one or more embodiments may be used as one or more of a drilling or drill-in fluid during the drilling of a wellbore. The oil-based drilling fluid mixed with the previously mentioned components may be used in a wellbore drilling operation to drill a wellbore in a subterranean zone. For example, multiple barrels of the oil-based drilling fluid may be prepared, each barrel mixed with the previously discussed components. The multiple barrels are introduced into a subterranean zone while drilling the wellbore in the subterranean zone.

Examples

The following examples are merely illustrative and should not be interpreted as limiting the scope of the present disclosure.

Materials and Synthesis:

The fatty acid methyl esters (hereafter “EME-FA”) used in these examples was VIKOFLEX® 9010 (Arkema), which contains epoxidized methyl oleate, epoxidized methyl linoleate, and epoxidized methyl alpha-linoleate.

In order to ascertain the ability of the EME-FA to function as a rheology modifier, invert OBMs having the compositions detailed in Table 1 were prepared. In the examples, 12 ppb (pounds per barrel) of the primary emulsifiers are used to formulate 80 pcf (per cubic feet) invert-emulsion oil based muds using Safra-oil as a base oil. Safra oil is a highly de-aromatized aliphatic solvent in the class of kerosene. The oil-water ratio is 70:30 by volume. “mL” means millilitres and “g” means grams.

TABLE 1 Compositions of exemplary drilling muds Formulation Example 1 Comparative Example 1 Safra oil (mL) 218 218 INVERMUL ® (mL) 12 12 EZ MUL ® (mL) 4 4 Lime (g) 6 6 GELTONE ® (g) 4 4 DURATONE ® (g) 6 6 Brine (mL) (61 g CaCl₂ 85 85 in 85 mL of water) Barite (g) 161 161 EME-FA (mL) 6 0 Characterization:

The OBM dispersions were hot rolled at 300° F. for 16 h under a pressure of 500 psi. After hot rolling, the OBMs were cooled to room temperature and a OFITE Model 900 viscometer (OFI Testing Equipment, Inc.) was utilized for testing their rheology. The rheological properties of Example 1 and Comparative Example 1 were measured at 49° C. and are reported in Table 2.

TABLE 2 Rheological properties of exemplary OBMs Property Example 1 Comparative Example 1 Plastic viscosity (PV) (cP) 31 22.9 Yield point (YP) (lb/100 ft²) 10.3 9.2 6-rpm reading (cP) 8.8 4.1 3-rpm reading (cP) 6.4 3.6 10 sec gel strength (lb/100 ft²) 9.1 5.2 10 min gel strength (lb/100 ft²) 13 10.8

The rheological features such as the plastic viscosity (PV) and yield point (YP) were estimated by using the values obtained from the dial readings of the viscometer at 600 rpm and 300 rpm. To measure the 10-second (initial) gel strength and the 10-minute (final) gel strength of the OBMs, the viscometer was operated at 600 rpm for 10 s and then stopped for 10 s and 10 min, respectively. Afterward, the viscometer operated at a revolution speed of 3 rpm and the dial reading was noted as the 10-sec and 10-min gel strength, respectively, in pounds per 100 ft².

Results and Discussion

The plastic viscosity and yield point are important properties that inform the suitability of an OBM for a given application. Table 2 indicates that the yield point of a drilling mud significantly increase after addition of the EME-FA and hot rolling at high temperature and pressure. This increased yield point indicates that Example 1 has an improved carrying capacity of cuttings as compared to Comparative Example 1. The inclusion of EME-FA only resulted in a small increase in plastic viscosity.

The low shear rheology of a drilling mud reflects its ability to suspend a solid material under while the shear is minimized or ceased. The rheology of Example 1 and Comparative Example 1 at 3-rpm and 6-rpm is reported in Table 2 and depicted in FIG. 3, which demonstrate that the addition of the EME-FA prominently enhances the low shear rheology of an OBM, as compared to a traditional drilling mud. Therefore, the addition of EME-FA provides an OBM having an enhanced solids-suspending capacity.

Similarly, the gel strength of a drilling mud reflects its ability to suspend a solid material under static conditions. It is a quantification of the attractive forces within the drilling mud system in the absence of flow. The gel strength of Example 1 and Comparative Example 1 is reported in Table 2 and depicted in FIG. 4, which demonstrate that the addition of the EME-FA prominently enhances the gel strength of an OBM after both 10 s and 10 min, as compared to a traditional drilling mud. Therefore, the addition of EME-FA provides an OBM having an enhanced solids-suspending capacity.

When either words “approximately” or “about” are used, this term may mean that there can be a variance in value of up to ±10%, of up to 5%, of up to 2%, of up to 1%, of up to 0.5%, of up to 0.1%, or up to 0.01%.

Although the preceding description has been described herein with reference to particular means, materials and embodiments, it is not intended to be limited to the particulars disclosed herein; rather, it extends to all functionally equivalent structures, methods and uses, such as those within the scope of the appended claims. 

What is claimed is:
 1. An invert oil-based mud (OBM), comprising: an oleaginous continuous phase; an aqueous internal phase; an emulsifier; and 0.1 to 5 wt. % (weight percent) based on a total weight of the invert OBM of a rheology modifier that comprises one or more of the group consisting of epoxidized methyl oleate, epoxidized methyl linoleate, and epoxidized methyl α-linolenate, wherein the invert OBM has a yield point (lb/100 ft²) greater than a reference yield point of a reference invert OBM, wherein the reference invert OBM has the same composition as the invert OBM but does not include the rheology modifier.
 2. The invert OBM according to claim 1, wherein the rheology modifier comprises epoxidized methyl oleate, epoxidized methyl linoleate, and epoxidized methyl α-linolenate.
 3. The invert OBM according to claim 1, wherein the invert OBM has a plastic viscosity of the range of 20 to 40 cP (centipoise).
 4. The invert OBM according to claim 1, wherein the invert OBM has a yield point of the range of 5 to 15 lb/100 ft² (pounds per 100 square feet).
 5. The invert OBM according to claim 1, wherein the invert OBM has an initial gel strength after 10 seconds of the range of 5 to 15 lb/100 ft².
 6. The invert OBM according to claim 1, wherein the invert OBM has a final gel strength after 10 minutes of the range of 10 to 20 lb/100 ft².
 7. A method of using an invert oil-based mud (OBM) in a wellbore, comprising: introducing the invert OBM into the wellbore, the invert OBM comprising an oleaginous continuous phase; an aqueous internal phase; an emulsifier; and 0.1 to 5 wt. % based on a total weight of the invert OBM of a rheology modifier that comprises one or more selected from the group consisting of epoxidized methyl oleate, epoxidized methyl linoleate, and epoxidized methyl alpha-linolenate, wherein the invert OBM has a yield point (lb/100 ft²) greater than a reference yield point of a reference invert OBM, wherein the reference invert OBM has the same composition as the invert OBM but does not include the rheology modifier.
 8. The method according to claim 7, wherein the emulsifier comprises epoxidized methyl oleate, epoxidized methyl linoleate, and epoxidized methyl α-linolenate.
 9. The method according to claim 7, wherein the invert OBM has a plastic viscosity of the range of 20 to 40 cP.
 10. The method according to claim 7, wherein the invert OBM has a yield point of the range of 5 to 15 lb/100 ft².
 11. The method according to claim 7, wherein the invert OBM has an initial gel strength after 10 seconds of the range of 5 to 15 lb/100 ft².
 12. The method according to claim 7, wherein the invert OBM has a final gel strength after 10 minutes of the range of 10 to 20 lb/100 ft². 